Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) narrated that the Noble Prophet (peace and blessings be upon him) led the prayer. (Ibrahim, the narrator, said: I do not know whether there was an addition or a reduction in the prayer.) Then, when he finished with salam, it was said to him, "O Messenger of Allah, has a new command come regarding the prayer?" He said, "What is the matter?" The people said, "You have performed such and such rak'ahs." Upon hearing this, he turned both his feet and faced the qiblah, and performed two prostrations (of forgetfulness), and then made salam. Then he turned towards us and said, "If a new command had been revealed regarding the prayer, I would have surely informed you beforehand. But I am only a human being like you; just as you forget, I also forget. Therefore, when I forget, remind me. And if anyone is in doubt during the prayer, then he should think about what is correct and complete the prayer accordingly, then after making salam, perform two prostrations (of forgetfulness)."